1 Field of the Invention
The present invention relates to slab furnaces and, more particularly, to induction-type slab reheating furnaces.
2. Description of the Prior Art
Metal slabs are reheated prior to certain shaping or treating operations, such as rolling the slab to a specified shape, or treating the slab to obtain selected properties as in the manufacture of stainless and silicon steel and titanium. The reheating process is typically carried out in a batch-type furnace having a refractory lining wherein the slab is heated to a controlled temperature.
In one type of furnace design, the reheating furnace is provided with a bottom opening receiving the slab. In the prior art, the slab was carried into the furnace by an electrohydraulically controlled slab handling apparatus which gripped the slab between two fingers and then elevated the slab into the furnace.
Early furnaces of this type had no door or other structure to cover the bottom opening or otherwise close the furnace. These furnaces therefore lost heat through this opening by convection and radiation. Consequently, there existed a temperature gradient in the furnace that was sufficiently sharp to cause faults and other defects in the metal that impaired the quality and consistency of the subsequently finished product. Subsequently, these bottom entry furnaces were provided with doors that were connected to the furnace by a horizontally arranged hinge. These doors provided a means of closing the bottom openings of the furnace and thereby retard the loss of heat from the furnace that resulted in the temperature gradient that adversely affected the quality and consistency of the workpiece.
Unfortunately, the doors known in the prior art had several disadvantages. For example, the doors were hinged directly to the furnace and were connected such that they pivoted about an axis that was substantially perpendicular to the longitudinal center axis of the furnace. Consequently, the hinges that formed the connection between the furnace and the door were exposed to the extreme temperatures of the furnace causing them to warp and otherwise deteriorate. Also, the prior doors were controlled by hydraulically activated mechanism that was electrically interlocked with the operation of the furnace charging mechanism but required an additonal, independant hydraulic system for the furnace. Consequently, the mechanism for closing the doors added considerable complexity and expense to the installation and maintenance of the furnace.
Accordingly, there existed a need for effectively closing bottom entry slab furnaces such that a more even temperature could be maintained within, and that would have a useful life that was commercially more acceptable than doors known in the prior art. Also, there was a need for doors of a simpler and more dependable design and that were less expensive to install and maintain. Accordingly, there existed a need in the prior art for efficiently closing bottom entry slab furnaces such that a more even temperature could be maintained within.